Electronic assemblies which include a circuit board having a plurality of electronic components attached thereto are widely used in the communications industry to manage the flow of data on a telecommunications network. These electronic assemblies must be able to manage a high data rate over significant periods of time (e.g., months) without any maintenance. One problem encountered with these electronic assemblies, as well as other types of electronic assemblies, is that the above described data management activity causes the electronic components to generate a significant amount of heat which can be detrimental to the electronic assembly and thus cause maintenance problems. As a result, these electronic assemblies must be cooled constantly in order to maintain acceptable operating temperatures to avoid maintenance problems.
Several different approaches have been utilized in an attempt to address the aforementioned cooling requirement. For example, one approach employs assisted cooling techniques to maintain the electronic assembly within acceptable temperature limits. These assisted cooling techniques typically involve externally-powered cooling devices, such as fans. In a telecommunication central office switch, large fans are employed to provide the necessary cooling to the electronic assemblies. However, the use of assisted cooling techniques are discouraged by the communications industry because assisted cooling techniques can introduce a hazard to technicians working in the area. For example, the use of large fans can undesirably create a hazardous noise level. In addition, the types of fans used in assisted cooling tend to break down and thus increase the maintenance problems associated with servicing the telecommunications network.
Another approach utilizes a liquid to cool the electronic components attached to the circuit board. However, several different kinds of electronic components are used on the circuit boards, and many of the electronic components can not be cooled by a liquid. For example, many optoelectronic devices, such as laser transmitters, are not amenable to liquid cooling. Accordingly, if liquid cooling is desirable in a circuit having components that are not amenable to liquid cooling, the air cooled components must be segregated from the liquid cooled environment. Such situations typically require separate air cooled and liquid cooled circuit boards.
In one such design, one or more circuit boards having electronic components thereon which can be cooled in a liquid environment are completely housed in a box filled with a cooling liquid. Such a design electrically interconnects the gas cooled or air cooled electronic components to the liquid cooled electronic components utilizing special insulated feedthroughs which must extend through a wall of the box so as to interface with the liquid cooled electronic components. These feedthroughs often introduce signal reflections and impedance discontinuities in the signal path, thereby limiting the bandwidth which can effectively be transmitted. In addition, these designs often suffer from the problem of leaks at the point where the feedthrough penetrates the box wall.
There is an additional need, therefore, for a method and arrangement for cooling an electronic assembly which overcomes one or more of the above discussed problems.